U.S. patent number 5,629,070 [Application Number 08/445,148] was granted by the patent office on 1997-05-13 for authentication label and authenticating pattern incorporating diffracting structure and method of fabricating them.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Hans E. Korth.
United States Patent |
5,629,070 |
Korth |
May 13, 1997 |
Authentication label and authenticating pattern incorporating
diffracting structure and method of fabricating them
Abstract
A light diffracting structure 10 in an authenticating pattern 20
especially for an authentication label 30 is used for
authenticating and protecting against forgery various valuable
objects. The light diffracting structure 10 has unique parameters
generating a uniquely colored pattern. The unique parameters are
randomly defined by anisotropic process steps during the
manufacturing of the diffracting structure and are not under full
control of the producer. This prevents copying or creating an exact
replica thereof. The authenticating pattern 20 comprises an
integrated structure of a substrate layer 21 and a transparent
overcoat layer 22 and the viewable interface therebetween includes
the light diffracting structure 10. The uniquely colored
authenticating pattern can be verified by simple observation with
the naked eye which is a prerequisite for ubiquitous
verification.
Inventors: |
Korth; Hans E. (Stuttgart,
DE) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
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Family
ID: |
8216446 |
Appl.
No.: |
08/445,148 |
Filed: |
May 19, 1995 |
Foreign Application Priority Data
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Nov 9, 1994 [EP] |
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94117660 |
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Current U.S.
Class: |
428/174; 359/2;
428/212; 428/167; 428/166; 428/143; 428/142; 428/195.1;
428/170 |
Current CPC
Class: |
G02B
5/1857 (20130101); G03H 1/041 (20130101); G06K
19/06046 (20130101); G06K 19/16 (20130101); B42D
25/29 (20141001); B42D 25/328 (20141001); G02B
5/1861 (20130101); Y10T 428/24372 (20150115); G03H
1/0011 (20130101); G03H 1/0244 (20130101); G03H
2240/50 (20130101); Y10T 428/24802 (20150115); Y10T
428/24595 (20150115); Y10T 428/24364 (20150115); Y10T
428/24942 (20150115); Y10T 428/24628 (20150115); Y10T
428/2457 (20150115); Y10T 428/24562 (20150115) |
Current International
Class: |
B42D
15/00 (20060101); B42D 15/10 (20060101); G02B
5/18 (20060101); G03H 1/04 (20060101); G06K
19/06 (20060101); G06K 19/14 (20060101); G06K
19/16 (20060101); B32B 001/00 (); B32B
003/00 () |
Field of
Search: |
;428/411.1,913,914,142,143,166,167,170,174,187,195,212 ;359/2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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2093404 |
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Sep 1982 |
|
GB |
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WO87/07034 |
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Nov 1987 |
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WO |
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Primary Examiner: Krynski; William
Attorney, Agent or Firm: Morris; Daniel P.
Claims
I claim:
1. A light diffracting structure having parameters generating a
visibly distinguishable colored pattern that is used to validate
the authenticity of an object attached to the structure wherein
said parameters are randomly defined by anisotropic process steps
during the manufacturing of said diffracting structure.
2. The light diffracting structure of claim 1
wherein said light diffracting structure comprises a structure in
the form of a relief grating and an arrangement of periodic areal
structure elements in the light diffracting structure.
3. The light diffracting structure of claim 2
wherein said parameters comprise the peak-to-valley ratio b:a and
the line depth c of the relief grating.
4. An authenticating pattern for an object comprising
an integrated structure of a substrate layer and a transparent
overcoat layer formed on the object,
the layers defining a viewable interface therebetween including a
light diffracting structure randomly defined by anisotropic steps
during the manufacture of the diffracting structure to produce a
visibly distinguishable colored pattern that is used to validate
the authenticity of the object.
5. The authenticating pattern of claim 4
wherein said transparent overcoat layer is bonded to said substrate
layer in a manner sufficiently secure to prevent said overcoat
layer from being removed from said substrate layer without
destroying said substrate layer.
6. The light diffracting structure of claim 4
wherein said light diffracting structure includes a structure in
the form of a relief grating.
7. The light diffracting structure of claim 6
wherein said parameters comprise the peak-to-valley ratios b:a and
the line depths c of the relief grating.
8. An authentication label as part of an object comprising:
a) an integrated structure of a substrate layer and a transparent
overcoat bonded to the substrate layer to define therebetween a
viewable interface including a light diffracting structure randomly
produced by an anisotropic process during the manufacture of the
diffracting structure to produce a visibly identifiable
authenticating pattern; and
b) graphic personalization information formed in said integrated
structure.
9. The authentication label of claim 8,
wherein said authentication label is substantially circular in
shape and the authenticating patterns are concentrically arranged
around the graphic personalizing information provided in the center
of the circle.
10. The authentication label of claim 9,
wherein said graphic personalizing information comprises a
hologram.
11. The light diffracting structure of claim 10,
wherein said light diffracting structure includes a relief
grating.
12. The light diffracting structure of claim 11,
wherein said parameters include the peak-to-valley ratios b:a and
the line depths c of the relief grating.
13. The authenticating pattern of claim 12
wherein said light diffracting structure has more than approximate
2000 lines/mm to assure total internal reflectance within said
overcoat layer.
14. The authenticating pattern of claim 5
wherein said integrated structure further comprises a metal layer
overcoating said diffracting structure.
15. The authenticating pattern of claim 13
wherein the material of said substrate layer and said overcoat
layer comprise transparent amorphous materials.
16. The light diffracting structure of claim 8
wherein said graphic personalization information is contained in
both said substrate layer and said transparent overcoat.
Description
FIELD OF THE INVENTION
This invention relates to a light diffracting structure and to an
authenticating pattern especially for use in an authentication
label for authenticating and protecting against forgery various
valuable objects such as bank notes, credit cards, identification
documents, authentication master plates, brand products or
phonographic records.
It also relates to a process for fabricating the diffraction
structure, the authenticating pattern and the authentication
label.
BACKGROUND OF THE INVENTION
Sealing is a technique as old as civilization. It identifies the
owner and indicates the integrity of an object. A written message
becomes a document due to a sealing process. Today, sealing and
printing techniques are used to avoid unauthorized replication of
mass produced objects. However, an increasing economic damage
results from forgery due to insufficient security. Security of the
sealing process requires that a seal cannot be copied and that the
seal stamper or printing plate are held under control. Removal of
the seal should lead to its destruction when protection against
transfer of seals is needed.
A complex engraved pattern is required to protect against forgery.
Nevertheless, every structure created by human beings can be
replicated with the necessary skill, information, equipment and
time. Typically, the effort to recreate a seal stamper or printing
plate will be similar or less than the effort for the production of
the original. This has lead to an ever increasing complexity of the
sealing process for valuable objects. Holograms can be used as an
additional protection.
For authenticating documents and things U.S. Pat. No. 5,145,212
teaches the use of non-continuous reflective holograms or
diffraction gratings. Such a hologram or diffraction grating is
firmly attached to a surface that contains visual information
desired to be protected from alteration. The reflective
discontinuous hologram is formed in a pattern that both permits
viewing the protected information through it and the viewing of an
authenticating image or other light pattern reconstructed from it
in reflection. In another specific authentication application of
this US Patent a non-transparent structure of two side-by-side
non-continuous holograms or diffraction patterns, each
reconstructing a separate image or other light pattern, increases
the difficulty of counterfeiting the structure.
PCT application WO87/07034 describes holograms, including
diffraction gratings, that reconstruct an image which changes as
the hologram is tilted with respect to the viewer and in a manner
that images reconstructed from copies made of the hologram in
monochromatic light do not have that motion.
In UK Patent Application GB 2 093 404 sheet material items which
are subject to counterfeiting have an integral or bonded
authenticating device which comprises a substrate having a
reflective diffractive structure formed as a relief pattern on a
viewable surface thereon and a transparent material covering the
structure. Specified grating parameters of the diffractive
structure result in peculiar, but easily discernable, optical
colour properties that cannot be copied by colour copying
machines.
U.S. Pat. No. 4,661,983 describes a random-pattern of microscopic
lines or cracks having widths in the order of micrometers that
inherently forms in a dielectric coating layer of an authenticating
device incorporated in a secure document. It permits identification
of a genuine individual document by comparing read-out
line-position information derived by microscopic inspection with
read-out digital codes of line-information obtained earlier at the
time of fabrication of the document.
The digital data of the random cracks being stored after
microscopically inspecting the document these data are used for the
fabrication of cracks if the random pattern does not inherently
develop.
Although these examples make forging more difficult, they can give
no absolute protection. The digital data may be copied and the
hologram information may be copied photographically or the hologram
may be recreated. Minor deviations of holograms cannot be
determined easily, as the extended non-monochromatic illumination
within a real-world environment tends to reproduce hologram images
with fuzzy shapes and colours.
Forgery of money causes significant economic loss. The advent of
high quality copy machines severely threatens many currencies.
Identification documents like passports, identity cards or drivers
licenses are used for different purposes, also for governmentally
regulated purposes.
Credit cards or corporate badges identify the owner of an account
or the employee of a company. In all these cases the document must
combine information of the bearer with the authorization
information from the issuing organization. An authentication label
with personalization on identification documents helps to eliminate
the risk to accept an invalid document and with the invention as
claimed a machine-based verification is not necessary.
The protection of brand labels has long been a problem.
Distribution packages for computer software, in particular, are
highly threatened by forgery as the costs for the replication of
the package, for example a CD-ROM, are low in comparison with the
value of the copied data. An authenticating pattern or
authentification label on the data carrier would allow the customer
to purchase authorized products and it would allow him to prove the
ownership at a legally fabricated product. If all the products of a
class or brand were marketed with a personalized authentificating
pattern or authentification label, the ownership claim for a stolen
object like e.g. an automobile can be verified from an intact
pattern or label. A missing pattern or label would indicate
manipulation. The exchange of an authentificating pattern or
authentification label would not make sense as it requires the
possession of an identical product.
A unique pattern or label embedded into a write-once or read-only
type data carrier allows to prove the integrity of large sets of
coded data. With a reference to the authentificating pattern code
or to the authentification label code stored with the data, it is
not possible to copy modified data onto an identical data carrier.
Attempts to modify data on the original carrier makes no sense as
it affects e.g. checksums and other criteria. A forge-proof
authentificating pattern or authentification label allows the use
of large encoded databases like catasters, patent data bases or
financial files as legally approved documents.
All these examples show that equipped with the authenticating
pattern or the authentication label objects like money bills,
passports, credit cards etc. gain maximum protection against
forgery.
Master plates of the authenticating pattern testify the
authorization of the label manufacturer.
It is therefore an object of the present invention to provide a
light diffracting structure, an authenticating pattern and an
authentication label with perceivable parameters where there is no
way to directly copy or to recreate the light diffraction
structure, the pattern, or the label.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with the present invention, a light diffracting
structure has parameters generating a visually identifiable colored
pattern where the parameters are randomly defined by anisotropic
process steps during the manufacturing of the diffracting
structure. An authenticating pattern of the present invention
comprises an integrated structure of a substrate layer and a
transparent overcoat layer forming the light diffracting structure
as a viewable interface therebetween. An authentication label
includes at least one such authenticating pattern which contains
personalizing information like pictorial and/or alphanumeric
information. An authenticating pattern or an authentication label
incorporating such a diffracting structure with randomly defined
parameters is not under full control of the producer. Therefore,
not even the producer or owner of an original authenticating
pattern can copy it or create an exact replica thereof. The
uniquely colored authenticating pattern can be verified by simple
observation with the naked eye; thus simplifying the recognition by
making use of the unsurpassed image processing properties of the
human eye. This visual access to an authenticating pattern or an
authentication label without a special illumination or equipment is
a prerequisite for ubiquitous verification.
BRIEF DESCRIPTION OF THE DRAWINGS
Ways of carrying out the invention are described in detail below
with reference to drawings showing only specific embodiments in
which:
FIG. 1 schematically shows an embodiment of a light diffracting
structure in form of a relief grating with some of the most
important parameters;
FIG. 2 shows a prior art example of a diffraction pattern or
diffraction grating of a hologram and FIG. 2b illustrates
characteristic curves of the diffraction pattern of FIG. 2a;
FIG. 3 is a schematic diagram of an authenticating pattern with the
light diffracting structure of FIG. 1;
FIGS. 4a, 4b and 4c schematically illustrate embodiments of an
authentication label with the authenticating pattern of FIG. 3;
FIGS. 5a, 5b and 5c show different objects equipped with an
authentication label; and
FIG. 6 schematically illustrates a possible method for quantifying
the colour of the authentication label.
DETAILED DESCRIPTION
The light diffracting structure shown in FIG. 1 is a relief grating
10 with numerous grooves or pits which may have the same or
different groove or line depths c. Another important parameter of
the diffracting structure 10 is the peak-to-valley ratio b:a.
An optical phase grating like the relief grating of FIG. 1 reflects
incident light into various diffraction orders depending on the
wavelength of the light, the grid line density, the grid depth
which is the line depth c and the grid line profile or grid line
anisotropy which is the peak-to-valley ratio b:a.
The diffraction colour varies strongly with the line depth c. This
is shown in the prior art diffraction grating of hologram 29' of
FIG. 2a with three adjacent grating regions 47', 49' and 51'. In
this example the area 47' is constructed to have a groove depth
which is substantially that indicated at D3 in FIG. 2b. The amount
of light diffracted from that area into a blue component of the
first order diffracted beam is zero, while there is some intensity
in other colours. Similarly, the adjacent area 49' is made to have
a groove depth substantially equal to D4 indicated in FIG. 2b, thus
having no light diffracted in the green portion. Lastly, the region
51' is made to have a groove depth substantially equal to D5 of
FIG. 2b, thereby having substantially no intensity diffracted into
the red component of the first order diffracted beam.
The diffraction colours representable by the diffraction structure
10 can be used to design the authenticating patterns 30 of FIGS.
4a-4c that contain colour field information. By design these
colours may only be roughly determined, there are no "correct"
colours and there is no fuzziness due to imperfect replication.
Variations in the line depth c of some 10 nm can be observed easily
and an even higher sensitivity of about 5 nm can be achieved when
the visibility of the borderline between two similar grating
regions, areas or colour fields is judged.
The saturation of the diffraction colours depends on the
peak-to-valley ratio b:a of the diffracting structure 10. It gives
a highly sensitive colour field discrimination criterion. The
visual deviation of a nominally diffracting structure 10 depends
exclusively on the non-linearity of the manufacturing process.
The relative intensity of the diffraction colours depends on the
grid profile and the surface roughness or micro-roughness. The grid
profile comprises a widespread variety of different shaped
gridlines like rectangular gridlines or gridlines with rounded
corners.
Instead of a relief grating as shown in FIG. 1 the diffracting
structure may be an arrangement of periodic areal structure
elements.
The authenticating pattern 20 of FIG. 3 is an integrated structure
of a substrate layer 21 and an overcoat layer 22.
The interface between substrate layer 21 and overcoat layer 22 is
viewable and includes the light diffracting structure 10. If the
overcoat layer 22 covering the relief grating 10 is transparent,
light diffracted at angles above some 45 degrees may be caught
within the overcoat layer 22 due to total internal reflection as
indicated in FIG. 3, right side. For a grid or relief grating with
more than approximately 2000 lines/mm already the first order
diffraction will be caught. This high line density assures total
internal reflectance within the overcoat layer 22. In this case the
specularly reflected light appears in the interference colour that
is defined by the line depth c of the relief grating or grid. The
material of the substrate layer 21 and the overcoat layer 22
comprises transparent amorphous materials like polymers, resins and
artificial resins which may also be coloured. The transparent
overcoat layer 22 is bonded to said substrate layer 21 in a manner
sufficiently secure to prevent said overcoat layer 22 from being
removed from said substrate layer 21 without destroying said
substrate layer.
The integrated structure may comprise a metal layer overcoating
said diffracting structure. Especially in the fabrication of
compact disks a metal layer may be applied for high reflectance.
The metallization layer may be homogeneous or made from randomly
sputtered metal particles.
A bonding layer will provide the interface between the
authenticating pattern or authentification label containing one or
a plurality of the integrated structures and the object to be
protected.
If the metallization layer is not homogeneous and if the material
of the overcoat layer 22 and the bonding layer is identical, it
will be impossible to free the relief surface within the 10 nm
tolerance.
Alternatively, the relief grating may be filled with a transparent
material with different refractive index. This would further impede
the mechanical access to the undistorted relief. In this embodiment
a flat metal coating may be added.
FIGS. 4a to 4c show various kinds of authentication labels 30 with
authenticating patterns or colour fields 20 of FIG. 3. The
authentication labels 30 consist of at least one authenticating
pattern 20 or a distinct number of authenticating patterns allowing
several different kinds of geometrical arrangements and additional
personalizing information 31.
The authenticating patterns may be combined to form bigger uniform
colour fields or fields with colour gradients. Regular geometrical
arrangements help to memorize the colour shade crossover locations.
From the locations of characteristic shades a code number may be
derived and this number may be memorized or communicated with
ease.
A possible method for quantifying the colour of the authentication
label is indicated in FIG. 6. This method uses the fact that the
saturation of the diffraction colours depends on the peak-to-valley
ratio b:a of the diffracting structure 10.
Varying the peak-to-valley ratio continuously within a relief
structure 60 enhances the colour contrast until maximum colour
saturation is reached as shown by the colour saturation curve 61.
Using two relief structures with the peak-to-valley variation to
reach maximum contrast running into opposite directions and two
scales 62 easily allows to define an equality mark 63 which
represents a quantitative size. A system based on this effect would
allow the translation of random colours and shades into a numeric
code that allows quantitative pattern classification.
The personalizing information comprises pictorial or alphanumeric
information and/or holograms or holographic elements or any
combination thereof. A logo of the issuing authority could easily
be incorporated which facilitates the memorizing of the colour
pattern.
The authentication label offers a great variety of different
possible shapes. In the embodiments shown in FIGS. 4a to 4b the
authentification label 30 is substantially circular in shape and
the authenticating patterns 20 are concentrically arranged around
the personalizing information 31 provided in the center of the
circle. A substantially circular or rounded shape complicates or
impedes the peeling from the objects equipped with an
authentication label.
Although it is virtually impossible that the colour parameters
match accurately for a multitude of colour fields within an
authenticating pattern 30 shown in FIGS. 4a-4c, there are more
parameters that depend on the diffractive structure.
A macro-roughness superimposed over the grid pattern may be
modulated to produce areas in the surface of the diffractive
structure varying between specular and diffuse reflexion. In the
areas of specular reflexion the line depth c is nearly zero and
there are no diffraction colours to be observed. Specular
reflectance and diffuse scatter can be judged independently by
comparison with areas or fields of pure specular reflectance or
pure scatter.
The polarization state of the light reflected from the
authenticating pattern 20 results from the interaction of the
diffractive structure 10 and the overcoat layer 22. It is
wavelength dependent.
The shape of the gridlines and their anisotropy affects the
appearance of the diffracted light that leaves the overcoat layer
22 without total reflexion as indicated in FIG. 3, right side.
An appropriate design allows to prepare colour fields 20 that
exhibit characteristic colour changes as a function of the two tilt
angles.
The selection of the grid line direction allows to steer the
diffraction pattern individually for every location on the
authenticating pattern.
The characteristic absorption of the overcoat layer 22 as a
function of the wavelength affects the fate of the totally
reflected light. The variation of the colour with the incidence
angle depends on the refractive index of the overcoat layer.
The influence of the refractive index and the characteristic
absorption of the overcoat layer material restricts the options to
use alternative materials for a copy. The superposition of a number
of different grid structures allows arbitrary combinations of
colour effects.
Some possible objects, especially credit cards and identification
cards, which could be equipped with an authentication label 30 are
shown in FIGS. 5a to 5c. Various other valuable objects such as
bank notes, identification documents, authentication master plates,
brand products or phonographic records could also be equipped with
one or more of the authentication labels described above.
Methods for producing a diffracting structure or a master plate
will now be described in detail.
To generate the light diffracting structure 10 with high structure
density, the manufacturing technology for advanced semiconductor
products can be adapted.
A mask for the horizontal pattern of the light diffracting
structure may be generated from computer data. On a substrate a
layer of photoresist is deposited and the mask pattern is then
transferred into the photoresist layer. After development the
patterned resist layer is used as a mask during the step of etching
pits or grooves into the substrate. The etch depth defining the
line depth c of the relief grating 10 also depends on the size of
the apertures in the photoresist. Various techniques are available
to obtain an anisotropic etching characteristic, like wet etching
and photochemical etching. With photochemical etching the etch
depth may be affected by a locally variable illumination. After the
etching step being completed the patterned photoresist layer is
removed.
To obtain the authenticating pattern 20 an overcoat layer 22 is
deposited on the substrate and fills the pits.
The diffracting structure 10 obtained as described above may also
be used as a master plate for generating numerous identical
authenticating patterns 20. To achieve this, the pattern of the
diffracting structure is replicated in a substrate by stamping or
molding processes using the diffracting structure 10 as a master
plate. The substrate typically is of transparent polymeric
material. For individualization additional information may be
written into the molded relief by laser burning or other known
techniques. The extent of parameter variations of said
authenticating patterns caused by said replication step is
insignificant compared to the extent of parameter variations
defined by said anisotropic etching process step during the
manufacturing of the diffracting structure 10.
An additional effect preventing copying is the shrinking of
material after the molding process. The shrinking smoothens the
relief grating 10 and even if a copy of the relief structure were
possible, the preparation of a new master plate would require an
unshrinking and a relief-sharpening process. This seems not
feasible.
Submaster plates for generating authentication patterns may be
produced from the master plate by well-known replication
techniques. The submaster plate should obtain a personalization
pattern to prevent the production of another master plate. The
personalization may contain additional self-encoded information.
This allows to verify both the authenticity of the diffracting
structure as a master plate and the descendence from the master
plate.
To complete the authenticating pattern 20 an overcoat layer 22 is
deposited on the substrate 21 and fills the pits. Additional
personalizing information like pictorial or alphanumeric
information or any combination thereof is added to the substrate
layer 21 or to the overcoat layer 22 or to both of them. The
personalizing information may be written into said layers by laser
burning, by stamping or by molding processes.
According to the manufacturing methods described above with their
random process steps unique authenticating patterns or
authentification labels may be created with perceivable random
variation of the pattern or label. The random variation is large as
compared to the statistical variations during the replication
processes like stamping or molding and the randomization space is
too big for a systematic experimental recreation. All this avoids
an authenticating pattern or an authentication label of the
invention being copied directly or to produce a master plate from
the pattern or label.
* * * * *